1. Field of the Invention
This invention relates to improvements in a wave compression supercharger, and more particularly, to an improved rotor for such a device having vanes formed with an axially extending bead which are mounted round the circumference of the rotor with a non-uniform spacing therebetween.
2. Description of the Prior Art
A wave compression supercharger of the type to which this improvement applies generally includes a rotor having a plurality of axially extending vanes mounted on the outer circumference of the rotor. The rotor is mounted on a shaft that is driven from the crankshaft of the engine by way of a belt and pulley. Stator plates are located at the axial ends of the rotor and provide, by way of ports formed through their thickness, passageways for the flow of exhaust gases and air to the rotor.
The vanes extend radially outwardly from the outer surface of the rotor upon which they are mounted, and the outer ends of the rotor vanes are generally joined to a cylindrical shroud that extends axially along the length of the rotor. In this way, gas or air channels are defined along the rotor length by the space between the rotor vanes, in the circumferential sense; by the outer rotor surface and the inner surface of the shroud, in the radial sense; and by the stator plates at the opposite ends of the rotor, in the axial sense. Typically, the rotor vanes are thin, rectangular plates of sheet steel, usually about 0.030 inches thick, perhaps an inch wide and four inches long for a typical automotive application.
Exhaust gas from an internal combustion engine at a relatively high pressure is admitted to a compression wave supercharger through the gas inlet port formed through the thickness of a stator plate located at one end of the rotor. Exhaust gas at reduced pressure exits a compression wave supercharger through the exhaust ports formed in the gas stator plate, which ports are spaced circumferentially from the gas inlet ports and are generally somewhat larger at the axially opposite end of the turbocharger. Ambient air enters the turbocharger through an inlet port formed through thickness of an air stator plate, and compressed air at a higher pressure than ambient conditions exits the supercharger through air exit ports formed through the air stator plate, but spaced circumferentially from the air inlet port.
The essential function of the wave compression supercharger is to provide means for an exchange of energy from the high pressure exhaust engine gas to the ambient air, whereby the inlet air is compressed and admitted to the intake manifold of the engine and the engine exhaust gas is expanded and delivered back to the exhaust system of the vehicle. In realizing this energy exchange, the high pressure exhaust gas produces a compression wave front in the axially extending channels. This wave compresses the inlet air and pumps the air from the supercharger into the engine intake manifold. As the rotor turns, the individual axial channels are sequentially exposed, on the one rotor side, first to the exhaust gas inlet port and later, during the rotor cycle, to the exhaust gas outlet port. At the axially opposite rotor end, the axial channels are sequentially exposed first to the ambient air inlet port and later, during the rotor cycle, to the compressed air exit port.
It is essential in the design of wave compression superchargers to maintain minimal clearances among the various components that define and contain the air volume within the channels. Consequently, the channels experience a cyclic pressure cycle from a low pressure condition when ambient air pressure prevails within the channel, to an extreme wherein the exhaust gas pressure wave is progressing axially along the channel. During a single rotor cycle, typically, the channels experience two pressure cycles because the inlet and outlet ports on the gas and air stator plates are symmetrically arranged about the diameter of the stator plates.
A high frequency siren-like noise is an operating characteristic of a wave compression turbocharger and is recognized to be a serious problem in automotive usage. Air and gas leakage in a wave compression turbocharger, by way of clearances between the rotary and stationary parts, particularly in the vicinity of the stator plate ports and between the axial ends of the rotor and the inner surfaces of the stator plates, produces high frequency noise. A further source of noise is the resonant vibration of the gases within the rotor cells. Vibratory response of the thin walled vanes to the resonant excitation within the cells is a further source of unwanted noise.
The power of a spark ignition or compression ignition engine is directly limited by the amount of air that can be inducted into the engine during the intake stroke. The air induction can be increased by increasing the number and size of the cylinders, or, to save weight, by using a compressor to supercharge the cylinder with air or the air/gas mixture. A supercharged engine, therefore, has an overall higher compression ratio and the charge is increased in density and temperature at ignition, as compared to engines without supercharging. The purpose of supercharging, then, is to maximize the amount of air inducted into the engine. Air expands when heated; therefore, it is desirable that the compressed air exiting a supercharger and entering the intake manifold of an engine be at a relatively low temperature and at a relatively high pressure. In this way, the density of the air is increased and the flow into the engine maximized.
As the incoming shock wave enters the rotor cell from the engine exhaust side and progresses along the axis of the supercharger, mixing of the exhaust gas with the ambient air present within the cell usually occurs to some extent. It is an object of supercharger design practice to minimize this mixing and in this way to lessen the amount of exhaust engine gas that is readmitted to the engine with the compressed air that leaves the supercharger. This mixing and return of exhaust engine gas is known as exhaust gas recirculation and should be held to a minimum for reasons of economy of operation and environmental protection.
In order to reduce the temperature of the air exiting the compressor and before its induction into the engine, engine cooling water is circulated through an aftercooler to remove heat from the air and, in this way, to reduce its volume, thereby increasing the flow rate of air into the engine. The temperature of the air that is compressed in and pumped from the supercharger is, therefore, a measure of the amount of exhaust gas recirculation. Preferably, the temperature of the air delivered to the engine is held to a minimum.